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QUESTION NO:7
Which statement is true about TCN propagation?
A. The originator of the TCN immediately floods this information through the network.
B. The TCN propagation is a two step process.
C. A TCN is generated and sent to the root bridge.
D. The root bridge must flood this information throughout the network.
Answer: C
Explanation:
Explanation
New Topology Change Mechanisms
When an 802.1D bridge detects a topology change, it uses a reliable mechanism to first notify the
root bridge.
This is shown in this diagram:
Once the root bridge is aware of a change in the topology of the network, it sets the TC flag on the
BPDUs it sends out, which are then relayed to all the bridges in the network. When a bridge
receives a BPDU with the TC flag bit set, it reduces its bridging-table aging time to forward delay
seconds. This ensures a relatively quick flush of stale information. Refer to Understanding
Spanning-Tree Protocol Topology Changes for more information on this process. This topology
change mechanism is deeply remodeled in RSTP. Both the detection of a topology change and its
propagation through the network evolve.
Topology Change Detection
In RSTP, only non-edge ports that move to the forwarding state cause a topology change. This
means that a loss of connectivity is not considered as a topology change any more, contrary to
802.1D (that is, a port that moves to blocking no longer generates a TC). When a RSTP bridge
detects a topology change, these occur:
It starts the TC While timer with a value equal to twice the hello-time for all its non-edge
designated ports and its root port, if necessary.
It flushes the MAC addresses associated with all these ports.
Note: As long as the TC While timer runs on a port, the BPDUs sent out of that port have the TC
bit set.
BPDUs are also sent on the root port while the timer is active.
Topology Change Propagation
When a bridge receives a BPDU with the TC bit set from a neighbor, these occur:
It clears the MAC addresses learned on all its ports, except the one that receives the topology
change.
It starts the TC While timer and sends BPDUs with TC set on all its designated ports and root port
(RSTP no longer uses the specific TCN BPDU, unless a legacy bridge needs to be notified).
This way, the TCN floods very quickly across the whole network. The TC propagation is now a one
step process. In fact, the initiator of the topology change floods this information throughout the
network, as opposed to 802.1D where only the root did. This mechanism is much faster than the
802.1D equivalent. There is no need to wait for the root bridge to be notified and then maintain the
topology change state for the whole network for seconds.
In just a few seconds, or a small multiple of hello-times, most of the entries in the CAM tables of
the entire network (VLAN) flush. This approach results in potentially more temporary flooding, but
on the other hand it clears potential stale information that prevents rapid connectivity restitution.
Reference
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml
QUESTION NO:29
What is the first thing that happens when IPv6 is enabled on an interface on a host?
A. A router solicitation is sent on that interface.
B. There is a duplicate address detection on the host interface.
C. The link local address is assigned on the host interface.
D. A neighbor redirect message is sent on the host interface.
Answer: B
Explanation:
Duplicate address detection (DAD) is used to verify that an IPv6 home address is unique on the
LAN before assigning the address to a physical interface (for example, QDIO). z/OS
Communications Server responds to other nodes doing DAD for IP addresses assigned to the
interface.
Reference
http://publib.boulder.ibm.com/infocenter/zos/v1r12/index.jsp?topic=/com.ibm.zos.r12.hale001
/ipv6d0021002145.htm
QUESTION NO:33
Which two OSPF LSA types are new in OSPF version 3? (Choose two.)
A. Link
B. NSSA external
C. Network link
D. Intra-area prefix
E. AS domain
Answer: A,D
Explanation:
New LSA Types
OSPFv3 carries over the seven basic LSA types we\’re familiar with from OSPFv2. However, the
type 1 and 2 LSAs have been re-purposed, as will be discussed in a bit. OSPFv3 also introduces
two new LSA types: Link and Intra-area Prefix.
Reference
http://packetlife.net/blog/2010/mar/2/ospfv2-versus-ospfv3/
QUESTION NO:17
Which three combinations are valid LACP configurations that will set up a channel? (Choose
three.)
A. On/On
B. On/Auto
C. Passive/Active
D. Desirable/Auto
E. Active/Active
F. Desirable/Desirable
Answer: A,C,E
Explanation:
QUESTION NO:10
Which command is used to enable EtherChannel hashing for Layer 3 IP and Layer 4 port-based
CEF?
A. mpls ip cef
B. port-channel ip cef
C. mpls ip port-channel cef
D. port-channel load balance
E. mpls ip load-balance
F. ip cef EtherChannel channel-id XOR L4
G. ip cef connection exchange
Answer: D
Explanation:
QUESTION NO:11
When you are troubleshooting duplex mismatches, which two errors are typically seen on the full-
duplex end? (Choose two.)
A. runts
B. FCS errors
C. interface resets
D. late collisions
Answer: A,B
Explanation:
QUESTION NO:30
What is the flooding scope of an OSPFv3 LSA, if the value of the S2 bit is set to 1 and the S1 bit is
set to 0?
A. link local
B. area wide
C. AS wide
D. reserved
Answer: C
Explanation:
The Type 1 router LSA is now link local and the Type 2 Network LSA is AS Wide
S2 and S1 indicate the LSA\’s flooding scope. Table 9-1 shows the possible values of these two
bits and the associated flooding scopes.
Table 9-1 S bits in the OSPFv3 LSA Link State Type field and their associated flooding scopes
LSA Function Code, the last 13 bits of the LS Type field, corresponds to the OSPFv2 Type field.
Table 9-2 shows the common LSA types used by OSPFv3 and the values of their corresponding
LS Types. If you decode the hex values, you will see that the default U bit of all of them is 0. The S
bits of all LSAs except two indicate area scope. Of the remaining two, AS External LSAs have an
AS flooding scope and Link LSAs have a linklocal flooding scope. Most of the OSPFv3 LSAs have
functional counterparts in OSPFv2; these OSPFv2 LSAs and their types are also shown in Table
9-2.
Table 9-2 OSPFv3 LSA types and their OSPFv2 counterparts
Reference
http://www.networkworld.com/subnets/cisco/050107-ch9-ospfv3.html?page=1
QUESTION NO:32
Which two tunneling techniques support IPv6 multicasting? (Choose two.)
A. 6to4
B. 6over4
C. ISATAP
D. 6PE
E. GRE
Answer: B,E
Explanation:
When IPv6 multicast is supported (over a 6to4 tunnel), an IPv6 multicast routing protocol must be
used
Restrictions for Implementing IPv6 Multicast
IPv6 multicast for Cisco IOS software uses MLD version 2. This version of MLD is fully backward-
compatible with MLD version 1 (described in RFC 2710). Hosts that support only MLD version 1
will interoperate with a router running MLD version 2. Mixed LANs with both MLD version 1 and
MLD version 2 hosts are likewise supported.
IPv6 multicast is supported only over IPv4 tunnels in Cisco IOS Release 12.3(2)T, Cisco IOS
Release 12.2
(18)S, and Cisco IOS Release 12.0(26)S.
When the bidirectional (bidir) range is used in a network, all routers in that network must be able to
understand the bidirectional range in the bootstrap message (BSM).
IPv6 multicast routing is disabled by default when the ipv6 unicast-routing command is configured.
On Cisco Catalyst 6500 and Cisco 7600 series routers, the ipv6 multicast-routing also must be
enabled in order to use IPv6 unicast routing
Reference http://www.cisco.com/web/about/ac123/ac147/ac174/ac197/
about_cisco_ipj_archive_article09186a00800c830a.html
http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-multicast.html
https://supportforums.cisco.com/thread/183386
QUESTION NO:25
Refer to the exhibit.
After a link flap in the network, which two EIGRP neighbors will not be queried for alternative
paths? (Choose two.)
A. 192.168.1.1
B. 192.168.3.7
C. 192.168.3.8
D. 192.168.3.6
E. 192.168.2.1
F. 192.168.3.9
Answer: B,C
Explanation:
Explanation
Both 192.168.3.7 and 192.168.3.8 are in an EIGRP Stub area
The Enhanced Interior Gateway Routing Protocol (EIGRP) Stub Routing feature improves network
stability, reduces resource utilization, and simplifies stub router configuration.
Stub routing is commonly used in a hub and spoke network topology. In a hub and spoke network,
one or more end (stub) networks are connected to a remote router (the spoke) that is connected to
one or more distribution routers (the hub). The remote router is adjacent only to one or more
distribution routers. The only route for IP traffic to follow into the remote router is through a
distribution router. This type of configuration is commonly used in WAN topologies where the
distribution router is directly connected to a WAN. The distribution router can be connected to
many more remote routers. Often, the distribution router will be connected to 100 or more remote
routers. In a hub and spoke topology, the remote router must forward all nonlocal traffic to a
distribution router, so it becomes unnecessary for the remote router to hold a complete routing
table. Generally, the distribution router need not send anything more than a default route to the
remote router.
When using the EIGRP Stub Routing feature, you need to configure the distribution and remote
routers to use EIGRP, and to configure only the remote router as a stub. Only specified routes are
propagated from the remote (stub) router. The router responds to queries for summaries,
connected routes, redistributed static routes, external routes, and internal routes with the message
“inaccessible.” A router that is configured as a stub will send a special peer information packet to
all neighboring routers to report its status as a stub router. Any neighbor that receives a packet
informing it of the stub status will not query the stub router for any routes, and a router that has a
stub peer will not query that peer. The stub router will depend on the distribution router to send the
proper updates to all peers.
Reference
http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/eigrpstb.html#wp1021949
QUESTION NO:16
In 802.1s, how is the VLAN to instance mapping represented in the BPDU?
A. The VLAN to instance mapping is a normal 16-byte field in the MST BPDU.
B. The VLAN to instance mapping is a normal 12-byte field in the MST BPDU.
C. The VLAN to instance mapping is a 16-byte MD5 signature field in the MST BPDU.
D. The VLAN to instance mapping is a 12-byte MD5 signature field in the MST BPDU.
Answer: C
Explanation:
MST Configuration and MST Region
Each switch running MST in the network has a single MST configuration that consists of these
three attributes:
1. An alphanumeric configuration name (32 bytes)
2. A configuration revision number (two bytes)
3. A 4096-element table that associates each of the potential 4096 VLANs supported on the
chassis to a given instance.
In order to be part of a common MST region, a group of switches must share the same
configuration attributes.
It is up to the network administrator to properly propagate the configuration throughout the region.
Currently, this step is only possible by the means of the command line interface (CLI) or through
Simple Network
Management Protocol (SNMP). Other methods can be envisioned, as the IEEE specification does
not explicitly mention how to accomplish that step.
Note: If for any reason two switches differ on one or more configuration attribute, the switches are
part of different regions. For more information refer to the Region Boundary section of this
document.
Region Boundary
In order to ensure consistent VLAN-to-instance mapping, it is necessary for the protocol to be able
to exactly identify the boundaries of the regions. For that purpose, the characteristics of the region
are included in the BPDUs. The exact VLANs-to-instance mapping is not propagated in the BPDU,
because the switches only need to know whether they are in the same region as a neighbor.
Therefore, only a digest of the VLANs-toinstance mapping table is sent, along with the revision
number and the name. Once a switch receives a BPDU, the switch extracts the digest (a
numerical value derived from the VLAN-to-instance mapping table through a mathematical
function) and compares this digest with its own computed digest. If the digests differ, the port on
which the BPDU was received is at the boundary of a region.
In generic terms, a port is at the boundary of a region if the designated bridge on its segment is in
a different region or if it receives legacy 802.1d BPDUs. In this diagram, the port on B1 is at the
boundary of region A, whereas the ports on B2 and B3 are internal to region B:
MST Instances
According to the IEEE 802.1s specification, an MST bridge must be able to handle at least these
two instances:
One Internal Spanning Tree (IST)
One or more Multiple Spanning Tree Instance(s) (MSTIs)
The terminology continues to evolve, as 802.1s is actually in a pre-standard phase. It is likely
these names will change in the final release of 802.1s. The Cisco implementation supports 16
instances: one IST (instance 0) and 15 MSTIs.
show vtp status
Cisco switches “show vtp status” Field Descriptions has a MD5 digest field that is a 16-byte
checksum of the
VTP configuration as shown below
Router# show vtp status
VTP Version: 3 (capable)
Configuration Revision: 1
Maximum VLANs supported locally: 1005
Number of existing VLANs: 37
VTP Operating Mode: Server
VTP Domain Name: [smartports]
VTP Pruning Mode: Disabled
VTP V2 Mode: Enabled
VTP Traps Generation: Disabled
MD5 digest : 0x26 0xEE 0x0D 0x84 0x73 0x0E 0x1B 0x69
Configuration last modified by 172.20.52.19 at 7-25-08 14:33:43
Local updater ID is 172.20.52.19 on interface Gi5/2 (first layer3 interface fou)
VTP version running: 2
Reference
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfc.shtml
http://www.cisco.com/en/US/docs/ios-xml/ios/lanswitch/command/lsw-cr-book.pdf
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